Arm components for vehicles, such as suspension arms that connect car bodies with wheels or radius rods that connect sub frames to wheel side structures, need to have sufficient rigidities in order to resist or to transmit large forces that are applied in propelling or braking the vehicles.
An arm component such as those mentioned above is typically constituted of a tube with a specified outer diameter and a wall thickness having a connecting bracket welded on one end and a connecting collar welded on the other end, where the connecting bracket being connected to the wheel side structure and the connecting collar connected to a mounting shaft on the chassis side via a rubber bush inserted the inside thereof. However, such an arm component is undesirable not only because of its heavy weight and also because of its complexity of manufacturing processes as it requires welding as it consists of three parts, a tube, a bracket and a collar.
Of late, a press-formed suspension arm was proposed recently as shown in Patent Document 1. This suspension arm, although it has a large seat for spring in its middle part, having a cross-section perpendicular to its axial direction shaping like a rectangular box with one side of which is open, generally comprises a flat back member extending along its longitudinal direction and a pair of left and right arm half members drooping down from the left and right side of the back member. The suspension arm is press-formed, where each arm half member is simultaneously formed with a through hole at one end thereof to constitute a part to serve as said connection bracket or connection collar, as well as a connection indentation at a position away from said end. Further, the bottom wall of said connection indentations of both arms are welded together in order to connect the right and left half members. The suspension arm thus formed is advantageous in terms of its weight and from the standpoint of manufacturing process since it is press-formed from a single sheet of metal.